1. Field of the Invention
The present invention relates to DC motor speed and direction controllers generally and, more particularly, to a novel motor speed controller for permanent magnet DC motor applications.
2. Background Art
Motors for which the speed controller of the present invention are particularly suited are typically heavy-duty 12-volt, 24-volt, and 36-volt permanent magnet DC motors such as are used to drive small vehicles, wheelchairs, sweepers, conveyor belts, and power steering units, for example.
Known speed and direction controllers for such motors are typically relatively large and complex and, consequently, relatively expensive. In particular, such known controllers usually employ large switching relays, since means are generally not included to limit the currents which the relays switch. Other disadvantages of such known controllers are that they do not permit current limiting in both drive and regenerative modes and ramping rates may vary depending on how the operator of the equipment changes throttle control direction. In addition, many such known controllers have inadequate filtering of the switched currents in the drive transistors. Further, circuitry to assure that both drive and regenerative transistors are not on at the same time and to disable current limiting functions near the time the transistors are switched on or off is unnecessarily complicated.
Accordingly, it is a principal object of the present invention to provide a method and means by which the sequencing of transistor switching and current limit circuit disabling in a DC motor controller is simply and economically accomplished.
Another object of the invention is to provide a method and means by which current may be limited in both drive and regenerative modes of a DC motor controller.
An additional object of the invention is to provide a method and means by which a DC motor controller may provide ramping rates which are independent of how the equipment operator moves the throttle when changing direction.
Yet another object of the invention is to provide a method and means by which the currents switched by the relays in a DC motor controller are limited during switching.
Yet an additional object of the invention is to provide an improved arrangement of filter capacitors in a DC motor controller.
Other objects of the invention, as well as particular features and advantages thereof, will be, apparent from the following description and the accompanying drawing figures.